Advances in the immunology of heart transplantation

Role of autophagy in rejection after solid organ transplantation: A systematic review of the literature

Organ transplantation has long been recognized as an effective treatment for end-stage organ failure, metabolic diseases, and malignant tumors. However, graft rejection caused by major histocompatibility complex mismatch remains a significant challenge. While modern immunosuppressants have made significant strides in reducing the incidence and risk of rejection, they have not been able to eliminate it completely. The intricate mechanisms underlying transplant rejection have been the subject of intense investigation by transplant immunologists. Among these factors, autophagy has emerged as a key player. Autophagy is an evolutionarily conserved mechanism in eukaryotic cells that mediates autophagocytosis and cellular protection. This process is regulated by autophagy-related genes and their encoded protein families, which maintain the material and energetic balance within cells. Additionally, autophagy has been reported to play crucial roles in the development, maturation, differentiation, and responses of immune cells. In the complex immune environment following transplantation, the role and mechanisms of autophagy are gradually being revealed. In this review, we aim to explore the current understanding of the role of autophagy in solid organ rejection after transplantation. Furthermore, we delve into the therapeutic advancements achieved by targeting autophagy involved in the rejection process.

Protective effects of neutrophil serine protease inhibition against ischemia-reperfusion injury in lung or heart transplantation

Transplanted organs are inevitably exposed to ischemia-reperfusion (IR) injury, which is known to cause graft dysfunction. Functional and structural changes that follow IR tissue injury are mediated by neutrophils through the production of oxygen-derived free radicals, as well as from degranulation which entails the release of proteases and other pro-inflammatory mediators. Neutrophil serine proteases (NSPs) are believed to be the principal triggers of post-ischemic reperfusion damage. Extended preservation times for the transplanted donor organ correlate with heightened occurrences of vascular damage and graft dysfunction. Preservation with α1-antitrypsin, an endogenous inhibitor of NSPs, improves primary graft function after lung or heart transplantation. Furthermore, pre-operative pharmacological targeting of NSP activation in the recipient using chemical inhibitors suppresses neutrophilic inflammation in transplanted organs. Hence, effective control of NSPs in the graft and recipient is a promising strategy to prevent IR injury. In this review, we describe the pathological functions of NSPs in IR injury and discuss their pharmacological inhibition to prevent primary graft dysfunction in lung or heart transplantation.

Single-cell analysis of graft-infiltrating host cells identifies caspase-1 as a potential therapeutic target for heart transplant rejection

Aims

Understanding the cellular mechanisms underlying early allograft rejection is crucial for the development of effective immunosuppressant strategies. This study aims to investigate the cellular composition of graft-infiltrating cells during the early rejection stage at a single-cell level and identify potential therapeutic targets.

Methods

A heterotopic heart transplant model was established using enhanced green fluorescent protein (eGFP)-expressing mice as recipients of allogeneic or syngeneic grafts. At 3 days post-transplant, eGFP-positive cells infiltrating the grafts were sorted and subjected to single-cell RNA-seq analysis. Potential molecular targets were evaluated by assessing graft survival and functions following administration of various pharmacological inhibitors.

Results

A total of 27,053 cells recovered from syngrafts and allografts were classified into 20 clusters based on expression profiles and annotated with a reference dataset. Innate immune cells, including monocytes, macrophages, neutrophils, and dendritic cells, constituted the major infiltrating cell types (>90%) in the grafts. Lymphocytes, fibroblasts, and endothelial cells represented a smaller population. Allografts exhibited significantly increased proportions of monocyte-derived cells involved in antigen processing and presentation, as well as activated lymphocytes, as compared to syngrafts. Differential expression analysis revealed upregulation of interferon activation-related genes in the innate immune cells infiltrating allografts. Pro-inflammatory polarization gene signatures were also enriched in these infiltrating cells of allografts. Gene profiling and intercellular communication analysis identified natural killer cells as the primary source of interferon-γ signaling, activating inflammatory monocytes that displayed strong signals of major histocompatibility complexes and co-stimulatory molecules. The inflammatory response was also associated with promoted T cell proliferation and activation in allografts during the early transplant stages. Notably, caspase-1 exhibited specific upregulation in inflammatory monocytes in response to interferon signaling. The regulon analysis also revealed a significant enrichment of interferon-related motifs within the transcriptional regulatory network of downstream inflammatory genes including caspase-1. Remarkably, pharmacological inhibition of caspase-1 was shown to reduce immune infiltration, prevent acute graft rejection, and improve cardiac contractile function.

Conclusion

The single-cell transcriptional profile highlighted the crucial role of caspase-1 in interferon-mediated inflammatory monocytes infiltrating heart transplants, suggesting its potential as a therapeutic target for attenuating rejection.

Revolutionizing Heart Transplantation: A Multidisciplinary Approach to Xenotransplantation, Immunosuppression, Regenerative Medicine, Artificial Intelligence, and Economic Sustainability

Heart transplantation (HTx) stands as a life-saving intervention for patients with end-stage heart disease, but the field is fraught with numerous challenges that span from the scarcity of donor organs to long-term complications arising from immunosuppressive therapies. This comprehensive review article offers an in-depth exploration of the multifaceted aspects of HTx. The review covers groundbreaking advancements in xenotransplantation, enabled by cutting-edge genetic engineering techniques, and the promising role of stem cell therapies, particularly porcine mesenchymal stem cells, in cardiac regeneration. It also delves into the evolution and limitations of immunosuppressive therapies and the revolutionary potential of artificial intelligence (AI) and machine learning (ML) in enhancing donor-recipient matching and predicting patient outcomes. Economic considerations, especially in the context of rising healthcare costs, are examined to assess the sustainability of these advancements. The article further discusses the significant improvements in patient outcomes over the years, while highlighting persisting challenges, such as graft failure, rejection, and infection. It underscores the importance of experience and specialized training, evidenced by the presence of an institutional learning curve. The review concludes by advocating for a multifaceted, collaborative approach involving clinicians, researchers, and policymakers to overcome existing challenges. Through coordinated efforts that consider medical, ethical, and economic factors, the field of HTx is poised for further evolution, offering renewed hope for improved patient care and outcomes.

Multifunctional hydrogel modulates the immune microenvironment to improve allogeneic spinal cord tissue survival for complete spinal cord injury repair

Transplantation of allogeneic adult spinal cord tissues (aSCTs) to replace the injured spinal cord, serves as a promising strategy in complete spinal cord injury (SCI) repair. However, in addition to allograft immune rejection, damage-associated molecular pattern (DAMP)-mediated inflammatory microenvironments greatly impair the survival and function of transplants. In this study, we aimed to regulate the immune microenvironment after aSCT implantation by developing a functional hybrid gelatin and hyaluronic acid hydrogel (F-G/H) modified with cationic polymers and anti-inflammatory cytokines that can gelatinize at both ends of the aSCT to glue the grafts for perfect matching at defects. The F-G/H hydrogel exhibited the capacities of DAMP scavenging, sustainably released anti-inflammatory cytokines, and reduced lymphocyte accumulation, thereby modulating the immune response and enhancing the survival and function of aSCTs. When the hydrogel was used in combination with a systemic immunosuppressive drug treatment, the locomotor functions of SCI rats were significantly improved after aSCTs and F-G/H transplantation. This biomaterial-based immunomodulatory strategy may provide the potential for spinal cord graft replacement for treating SCI. STATEMENT OF SIGNIFICANCE: In this study, we aimed to regulate the immune microenvironment by developing a functional hybrid gelatin and hyaluronic acid hydrogel (F-G/H) modified with cationic polymers and anti-inflammatory cytokines that can gelatinize at both ends of the aSCT to glue the grafts for perfect matching at defects. We found that with the treatment of F-G/H hydrogel, the aSCT survival and function was significantly improved, as a result of reducing recruitment and activation of immune cells through TLR- and ST-2- related signaling. With the combination of immunosuppressive drug treatment, the locomotor functions of SCI rats were significantly improved after aSCTs and F-G/H transplantation. Findings from this work suggest the potential application of the F-G/H as a biomaterial-based immunoregulatory strategy for improving the therapeutic efficiency of the transplanted spinal cord graft for spinal cord injury repair.

Electrospun Carbon Nanotube-Based Scaffolds Exhibit High Conductivity and Cytocompatibility for Tissue Engineering Applications

Carbon nanotubes (CNTs) are known for their excellent conductive properties. Here, we present two novel methods, "sandwich" (sCNT) and dual deposition (DD CNT), for incorporating CNTs into electrospun polycaprolactone (PCL) and gelatin scaffolds to increase their conductance. Based on CNT percentage, the DD CNT scaffolds contain significantly higher quantities of CNTs than the sCNT scaffolds. The inclusion of CNTs increased the electrical conductance of scaffolds from 0.0 ± 0.00 kS (non-CNT) to 0.54 ± 0.10 kS (sCNT) and 5.22 ± 0.49 kS (DD CNT) when measured parallel to CNT arrays and to 0.25 ± 0.003 kS (sCNT) and 2.85 ± 1.12 (DD CNT) when measured orthogonally to CNT arrays. The inclusion of CNTs increased fiber diameter and pore size, promoting cellular migration into the scaffolds. CNT inclusion also decreased the degradation rate and increased hydrophobicity of scaffolds. Additionally, CNT inclusion increased Young's modulus and failure load of scaffolds, increasing their mechanical robustness. Murine fibroblasts were maintained on the scaffolds for 30 days, demonstrating high cytocompatibility. The increased conductivity and high cytocompatibility of the CNT-incorporated scaffolds make them appropriate candidates for future use in cardiac and neural tissue engineering.

The horizon of pediatric cardiac critical care

Pediatric Cardiac Critical Care (PCCC) is a challenging discipline where decisions require a high degree of preparation and clinical expertise. In the modern era, outcomes of neonates and children with congenital heart defects have dramatically improved, largely by transformative technologies and an expanding collection of pharmacotherapies. Exponential advances in science and technology are occurring at a breathtaking rate, and applying these advances to the PCCC patient is essential to further advancing the science and practice of the field. In this article, we identified and elaborate on seven key elements within the PCCC that will pave the way for the future.

Artesunate Restrains Maturation of Dendritic Cells and Ameliorates Heart Transplantation-Induced Acute Rejection in Mice through the PERK/ATF4/CHOP Signaling Pathway

Background

Heart transplantation (HT) is the only effective treatment for end-stage heart failure because it can effectively improve the survival rate and quality of life of patients with heart failure. Artesunate (ART) is an artemisinin derivative, with good water solubility and higher oral bioavailability. The main aim of this study was to determine the role of ART in HT mice.

Methods

In animal experiments, mice were divided into the control group, HT group, low ART+HT group, and high ART+HT group. Next, inflammatory cell infiltration, oxidative stress injury, and myocardial cell apoptosis were determined in heart tissue. The proportion of multiple lymphocytes in spleen and lymph nodes was then determined using flow cytometry. In addition, cell experiments were conducted to determine the changes in expression of surface maturation markers of BMDC and changes in intracellular reactive oxygen species after LPS stimulation. Finally, western blot analysis was performed to determine the levels of endoplasmic reticulum stress-related proteins (CHOP/ATF4/PERK).

Results

The survival time of mice in the ART treatment group was significantly prolonged and was positively correlated with the dose. In animal experiments, ART significantly reduced inflammatory cell infiltration in heart tissue and the proportion of CD4+CD8+ T cells in spleens and lymph nodes. Moreover, ART treatment lowered the 8-OHdg in hearts and myocardial apoptosis. In cell experiments, ART treatment slowed down the development and maturation of BMDCs by inhibiting the expression of endoplasmic reticulum stress-related proteins. Furthermore, the treatment alleviated the oxidative stress damage of BMDCs.

Conclusion

ART can inhibit maturation of dendritic cells through the endoplasmic reticulum stress signaling pathway, thereby alleviating acute rejection in mice after heart transplantation.

Investigation of hub genes and immune status in heart transplant rejection using endomyocardial biopsies

T cell‒mediated rejection (TCMR) and antibody‐mediated rejection (ABMR) are severe post‐transplantation complications for heart transplantation (HTx), whose molecular and immunological pathogenesis remains unclear. In the present study, the mRNA microarray data set GSE124897 containing 645 stable, 52 TCMR and 144 ABMR endomyocardial biopsies was obtained to screen for differentially expressed genes (DEGs) between rejected and stable HTx samples and to investigate immune cell infiltration. Functional enrichment analyses indicated roles of the DEGs primarily in immune‐related mechanisms. Protein‐protein interaction networks were then constructed, and ICAM1, CD44, HLA‐A and HLA‐B were identified as hub genes using the maximal clique centrality method. Immune cell infiltration analysis revealed differences in adaptive and innate immune cell populations between TCMR, ABMR and stable HTx samples. Additionally, hub gene expression levels significantly correlated with the degree and composition of immune cell infiltration in HTx rejection samples. Furthermore, drug‐gene interactions were constructed, and 12 FDA‐approved drugs were predicted to target hub genes. Finally, an external GSE2596 data set was used to validate the expression of the hub genes, and ROC curves indicated all four hub genes had promising diagnostic value for HTx rejection. This study provides a comprehensive perspective of molecular and immunological regulatory mechanisms underlying HTx rejection.

Kidney-induced systemic tolerance of heart allografts in mice

In swine and nonhuman primates, kidney allografts can induce tolerance of heart allografts, leading to their long-term, immunosuppression-free survival. We refer to this phenomenon as kidney-induced cardiac allograft tolerance (KICAT). In this study, we have developed a murine model for KICAT to determine the underlining cellular/molecular mechanisms. Here, we show that spontaneously accepted DBA/2J kidneys in C57BL/6 recipients induce systemic tolerance that results in the long-term acceptance of DBA/2J heart allografts but not third-party cardiac allografts. The state of systemic tolerance of hearts was established 2 weeks after transplantation of the kidney, after which time, the kidney allograft is no longer required. Depletion of Foxp3⁺ T cells from these mice precipitated rejection of the heart allografts, indicating that KICAT is dependent on Treg function. Acceptance of kidney allografts and cotransplanted heart allografts did not require the thymus. In conclusion, these data show that kidney allografts induce systemic, donor-specific tolerance of cardiac allografts via Foxp3 cells, and that tolerance is independent of the thymus and continued presence of the kidney allograft. This experimental system should promote increased understanding of the tolerogenic mechanisms of the kidney.

Accepted DBA/2J kidney allografts can confer acceptance of a co-transplanted DBA/2 heart allograft, which would be rejected when transplanted in the absence of the kidney graft.

Plasma CD5L and non-invasive diagnosis of acute heart rejection

BACKGROUND

Acute rejection is one of the most important direct contributors to mortality after heart transplantation. Advances in the development of novel non-invasive approaches for the early identification of allograft rejection are necessary. We conducted a non-targeted proteome characterization focused on identifying multiple plasmatic protein differences to evaluate their diagnostic accuracy for rejection episodes.

METHODS

We included consecutive plasma samples from transplant recipients undergoing routine endomyocardial biopsies. A liquid chromatography-tandem mass spectrometry analysis using isobaric tags (tandem mass tag 10-plex) was performed and concentrations of CD5L were validated using a specific sandwich enzyme-linked immunosorbent assay.

RESULTS

A total of 17 altered proteins were identified as potential markers for detecting heart transplant rejection, most involved in inflammation and immunity. CD5L, an apoptosis inhibitor expressed by macrophages, showed the best results in the proteomic analysis (n = 30). We confirm this finding in a larger patient cohort (n = 218), obtaining a great diagnostic capacity for clinically relevant rejection (≥Grade 2R: area under the curve = 0.892, p < 0.0001) and preserving the accuracy at mild rejection (Grade 1R: area under the curve = 0.774, p < 0.0001). CD5L was a strong independent predictor, with an odds ratio of 14.74 (p < 0.0001), for the presence of rejection.

CONCLUSIONS

Episodes of acute cardiac allograft rejection are related to significant changes in a key inhibitor of apoptosis in macrophages, CD5L. Because of its precision to detect acute cellular rejection, even at mild grade, we propose CD5L as a potential candidate to be included in the studies of molecule combination panel assays. This finding could contribute to improving the diagnostic and preventive methods for the surveillance of cardiac transplanted patients.